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We know that exercise may help improve thinking skills. But how much exercise? And for how long?

Seniors who exercised regularly performed better on thinking skills tests than those who did not.

To find the answers, researchers led by Joyce Gomes-Osman, Ph.D., PT, assistant professor of clinical physical therapy and neurology at the University of Miami Miller School of Medicine, reviewed all of the studies in which older adults were asked to exercise for at least four weeks and then take tests of thinking and memory skills. Their results were compared to those of people who did not start a new exercise routine. The review was published in the May 30 online issue of Neurology Clinical Practice, an official journal of the American Academy of Neurology.

The researchers found that people who exercised an average of at least 52 hours over about six months for about an hour each session may improve their thinking skills. In contrast, people who exercised for an average of 34 hours over the same time period did not show any improvement in their thinking skills.

The review did not find a relationship between a weekly amount of exercise and improved thinking skills.

“These results suggest that a longer-term exercise program may be necessary to gain the benefits in thinking skills,” said Gomes-Osman, the study’s author and director of the Neuromotor Plasticity Laboratory. “We were excited to see that even people who participated in lower-intensity exercise programs showed a benefit to their thinking skills. Not everyone has the endurance or motivation to start a moderately intense exercise program, but everyone can benefit even from a less-intense plan.”

The review included 98 randomized, controlled trials with a total of 11,061 participants, whose average age was 73. Of the total participants, 59 percent were categorized as healthy adults, 26 percent had mild cognitive impairment and 15 percent had dementia. A total of 58 percent did not regularly exercise before being enrolled in a study.

The researchers collected data on exercise session length, intensity, weekly frequency and amount of exercise over time. Aerobic exercise was the most common type of exercise, with walking the most common aerobic exercise; others including biking and dancing. Some studies used a combination of aerobic exercise along with strength, or resistance training and some used strength training alone. A small number of studies used mind-body exercises such as yoga or Tai chi.

After evaluating all of the data, the researchers found that in both healthy people and people with cognitive impairment, longer term exposure to exercise — at least 52 hours of exercise conducted over an average of about six months — improved the brain’s processing speed, the amount of time it takes to complete a mental task. In healthy people, that same amount of exercise also improved executive function, a person’s ability to manage time, pay attention and achieve goals. However, researchers found no link between the amount of exercise and improved memory skills. Aerobic exercise, strength training, mind-body exercise, and combinations of these were all found to be beneficial to thinking skills.

“Only the total length of time exercising could be linked to improved thinking skills,” said Gomes-Osman, “but our results may also provide further insight. With a majority of participants being sedentary when they first enrolled in a study, our research suggests that using exercise to combat sedentary behavior may be a reason why thinking skills improved.”

Future studies could further investigate which thinking abilities experience the greatest improvement with exercise. They could also look at the short-term and long-term effects of exercise in both sedentary and physically fit individuals.

Kai Hill is the manager of communications at the University of Miami Health System and the Miller School of Medicine.